1. Field of the Invention
The present invention relates to a distance measuring apparatus for measuring the distance to an object and, more particularly, to a distance measuring apparatus of an active type used in cameras and the like.
2. Related Background Art
The distance measuring apparatus of the active type used in the cameras and the like is normally constructed to detect the distance to the object in the following manner. First, an infrared emitting diode (hereinafter referred to as "IRED") projects a light beam toward the object and a position sensitive detector (hereinafter referred to as "PSD") detects reflected light of the thus projected beam. Output signals from this PSD are processed by signal processing circuits and a computing circuit and the computing circuit outputs the result of computation as distance data to a CPU. Then the CPU detects the distance to the object, based on this distance data.
Since there is the possibility of causing an error in distance measurement (ranging) based on only one light projection, it is conventional practice to employ a method of carrying out the light projection multiple times to generate a plurality of distance computation values and integrating the plurality of distance computation values with an integrating circuit provided with an integrating capacitor to effect averaging, as in the distance measuring apparatus described in Japanese Patent Application Laid-Open No. H10-281758. Then the CPU detects the distance to the object, based on distance data corresponding to the integration result of the integrating circuit.
The distance measuring apparatus constructed to integrate the distance computation values by use of the integrating capacitor, including the distance measuring apparatus described in the above Japanese application, however, had the following problem. Since the capacitor changes its capacitance with a change in ambient temperature, it posed the problem of ranging error. In addition, a capacitor has such characteristics as to change its capacitance with a lapse of time even in storage without being used, which was also the cause of the ranging error.